The present invention relates to an illuminator for use in ophthalmic surgery and more particularly to ophthalmic illuminator utilizing a variable-wedge rotating-disk attenuator to produce a light suitable for illuminating the inside of the eye.
Anatomically, the eye is divided into two distinct parts—the anterior segment and the posterior segment. The anterior segment includes the lens and extends from the outermost layer of the cornea (the corneal endothelium) to the posterior of the lens capsule. The posterior segment includes the portion of the eye behind the lens capsule. The posterior segment extends from the anterior hyaloid face to the retina, with which the posterior hyaloid face of the vitreous body is in direct contact. The posterior segment is much larger than the anterior segment.
The posterior segment includes the vitreous body—a clear, colorless, gel-like substance. It makes up approximately two-thirds of the eye's volume, giving it form and shape before birth. It is composed of 1% collagen and sodium hyaluronate and 99% water. The anterior boundary of the vitreous body is the anterior hyaloid face, which touches the posterior capsule of the lens, while the posterior hyaloid face forms its posterior boundary, and is in contact with the retina. The vitreous body is not free-flowing like the aqueous humor and has normal anatomic attachment sites. One of these sites is the vitreous base, which is a 3-4 mm wide band that overlies the ora serrata. The optic nerve head, macula lutea, and vascular arcade are also sites of attachment. The vitreous body's major functions are to hold the retina in place, maintain the integrity and shape of the globe, absorb shock due to movement, and to give support for the lens posteriorly. In contrast to aqueous humor, the vitreous body is not continuously replaced. The vitreous body becomes more fluid with age in a process known as syneresis. Syneresis results in shrinkage of the vitreous body, which can exert pressure or traction on its normal attachment sites. If enough traction is applied, the vitreous body may pull itself from its retinal attachment and create a retinal tear or hole.
Various surgical procedures, called vitreo-retinal procedures, are commonly performed in the posterior segment of the eye. Vitreo-retinal procedures are appropriate to treat many serious conditions of the posterior segment. Vitreo-retinal procedures treat conditions such as age-related macular degeneration (AMD), diabetic retinopathy and diabetic vitreous hemorrhage, macular hole, retinal detachment, epiretinal membrane, CMV retinitis, and many other ophthalmic conditions.
A surgeon performs vitreo-retinal procedures with a microscope and special lenses designed to provide a clear image of the posterior segment. Several tiny incisions just a millimeter or so in length are made on the sclera at the pars plana. The surgeon inserts microsurgical instruments through the incisions such as a fiber optic light source to illuminate inside the eye, an infusion line to maintain the eye's shape during surgery, and instruments to cut and remove the vitreous body.
During such surgical procedures, proper illumination of the inside of the eye is important. Typically, a thin optical fiber is inserted into the eye to provide the illumination. A light source, such as a metal halide lamp, a halogen lamp, a xenon lamp, or a mercury vapor lamp, is often used to produce the light carried by the optical fiber into the eye. Since such lamps cannot be easily dimmed while maintaining output performance and color balance, they are run at full power, and light intensity is varied by mechanical means. In varying the intensity of the light beam, it is important to maintain the beam diameter and only decrease the intensity of the beam. The light beam, whether attenuated or not, must be focused and aligned with the optical fiber that carries the beam into the eye.
Traditionally, the intensity of the light is varied by using mechanical louvers, camera variable aperture mechanisms, or neutral density filters. A mechanical louver operates like a set of Venetian blinds. The louvers are opened a certain amount to allow a certain amount of light to pass through. Such louvers, however, produce a series of bright and dark stripes in the resulting light beam. These can result in rings and other angular non-uniformities that appear in the beam emitted from the optical fiber. These non-uniformities deteriorate the quality of intraocular illumination. Likewise, the use of mechanical variable aperture mechanisms can also cause angular non-uniformities and an undesired narrowing of the width of the beam exiting the distal end of the fiber. Neutral density filters are often made of glass and block unwanted light. As they block light, they can heat up and crack. What is needed is an attenuator that does not decrease the diameter of the light beam or produce non-uniformities.